Recommendations

There is no best volume mode. The selection depends on your hardware and preference.

The most common choices are System Volume or Internal Volume.

Picking Between System Volume and Internal Volume

The determining factor in this decision is the type / quality of your hardware volume.

Sometimes turning up the hardware volume increases the noise you hear if you play silence (use 'Tools > Advanced Tools > Audio Calibration > Silence', and make sure 'Do not play silence' is not checked in Options > Audio). Test this by putting your ear right next to the speaker and adjust the System Volume while silence plays.

If the noise gets louder when you turn up the volume:

Use 'System Volume' so that you don't turn up the System Volume (which we found adds noise above) unless you have to

If the noise is unchanged when you turn up the volume:

Use 'Internal Volume' and leave the System Volume at 100%. This is advantageous because you get a 64bit volume and also because it allows Media Center to have as much signal headroom as possible, which is especially important if you do processing (upsampling, room correction, bass management, etc.)

Volume Protection

Volume Protection is a feature to prevent unexpectedly loud output. It is useful in cases where you connect Media Center to a high-gain amplifier where unexpected output at full volume could damage equipment or your ears.

Volume protection does the following:

Makes it so that it isn't possible to increase the volume by more than 5% at a time (so accidentally clicking 100% on the slider will not go to 100%)

Makes it so that the volume can not be increased by more than 20% a second

Makes it so that starting playback if nothing has played for 30 minutes sets the volume to 20% (unless the volume is already lower)

Startup Volume

In Options > Startup, there are a few volume related options under the header 'Startup Volume'.

Optimize volume for best sound quality
This option maximizes the wave-out volume slider on startup. This prevents double volume and related sound quality issues on Windows XP and earlier. The option is harmless but unnecessary on Vista and newer.

Set volume
This option will set the volume in Media Center to the specified level when launching the program.

Internal Volume Headroom

Internal Volume is particularly useful if you perform signal processing like Convolution, Equalization, Linkwitz, etc. Any volume reduction will be available as extra signal headroom, reducing the chances of unwanted clipping or volume reductions from Clip Protection.

Imagine that use convolution, which in rare cases outputs at +6dB (so over 100% peak level).

If you use System Volume, this +6dB will either have to be flat-lined (leading to audible distortion), or Clip Protection will engage and turn the volume of all channels down (also undesirable).

If you instead use Internal Volume, it's likely you will have headroom to avoid any clipping or volume reduction. For example, if you normally listen at -12dB, you could accommodate up to +12dB before there is any need for clipping or volume reductions.

Loudness

Loudness provides a more natural sounding volume control based on the frequency response characteristics of human hearing. It was added to MC18.

Reference Level Calibration

If you use Internal Volume, you may want to calibrate the volume control so that the zero point matches the "reference level."

The audio industry does not have a standard for playback system calibration, but in the movie industry a calibration standard has been defined by the Society of Motion Picture and Television Engineers (SMPTE). The standard states that a single channel pink noise signal with an RMS level of -20 dB relative to a full-scale sinusoid should be reproduced at 83 dB SPL.

To calibrate Media Center to this reference level:

Ensure that you have all speakers balanced relative to one another (normally using the distance and level sliders in DSP Studio > Room Correction)

Make sure you are using 'Internal Volume'

Disable 'Volume Levelling' in DSP Studio

Disable 'Loudness' (since it could color measurements)

Use Tools > Advanced Tools > Audio Calibration... and play the 'Volume calibration' clip using the channel count that most closely matches your hardware

Adjust the volume slider until a decibel meter reads 83 dB at the listening position playing from each speaker

If speakers read differently from one another, use DSP Studio > Room Correction to correct the relative speaker levels, then start this process again

Enter the volume level that delivers the reference level from the step above into Options > Audio > Volume > Internal volume reference level (the number is the volume slider percent value)

After this, the volume display will always be relative to this 'reference level.' This reference level will also be used if you enable 'Loudness'.